The present invention relates to an electrode for the electrochemical fine-boring of workpieces, including an electrode tube for an electrolyte to pass through to reach an electrically conductive workpiece which is to be machined, and an electrical conductor which is connected to the electrolyte, and to a process for producing an electrode for the electrochemical fine-boring of workpieces.
A conventional electrode for electrochemical boring includes a glass tube which is secured in a holding device, consists of SiO2 glass and through which an electrolyte flows. The electrolyte is brought into contact, through an opening in the glass tube which is opposite the holding device, with the area of a workpiece which is to be machined by boring. In the glass tube, there is an electrical conductor, to which a negative electric charge is applied via a DC source. The opposite, positive charge is applied to the workpiece, so that a chemical reaction leads to material being eroded at the area of the workpiece which is to be machined. The electrical conductor generally consists of a metal, such as a platinum wire.
A drawback of this arrangement is that when using glass tubes, the electrochemical boring is only able to produce holes or bores with a minimum diameter of 0.2 mm. Moreover, the electrode, which includes a glass tube and wire arranged therein, is of relatively complicated and sensitive construction.
It is an object of the present invention to provide an electrode that may be used to produce holes or bores with a very small diameter in combination with a simple electrode construction. Moreover, it is another object of the present invention to provide a process for producing such an electrode.
According to the present invention, the electrode tube is formed of a metal with a substantially amorphous structure, is electrically conductive and therefore simultaneously serves as an electrical conductor for applying a charge, and is provided on its outer surface, at least in sections, with a nonconductive insulating layer.
One advantage of an electrode made from a tube of this type is that metals of substantially amorphous structure, so-called metallic glass materials, may be processed to form tubes having relatively small external diameters in the range from 0.2 mm to 0.04 mm. Tubes produced from metal with a substantially amorphous structure are resistant to corrosion and wear and have a virtually smooth and flawless surface, along which the flow of electrolyte is optimal. Moreover, it is possible to eliminate the introduction of a metallic conductor, such as a platinum wire, since the negative charge of a DC source is applied to the tube itself. The positive charge of the DC source is applied to the workpiece which is to be machined.
The external diameter of the tube may be at most slightly less than 0.2 mm, and may be in the range from 0.2 mm to 0.04 mm, so that it is substantially possible to produce holes or bores with a diameter of 0.2 mm and below.
The tube may be of any desired cross-sectional geometry and may be adapted to various applications, so that it is also possible for holes which are not circular in cross section to be formed in the workpiece.
The tube may furthermore consist of a metallic solid glass, such as a ZrTiNiCuBe alloy, it also being possible to use other suitable alloys and therefore other metals which are of a substantially amorphous structure.
The nonconductive insulating layer may be a layer based on AlON or TiAlON or organic, such as coating, materials, or inorganic oxide ceramic, the layer thickness of this layer being very small. The thickness of the insulating layer may be less than 10 xcexcm and is generally between 4 xcexcm and 10 xcexcm. With an insulating layer based on TiAlON, the layer may be applied to the tube made from a metal of substantially amorphous structure by sputtering or vapor deposition.
The entire outer surface of the tube may be provided with a nonconductive insulating layer, in order to prevent electrochemical corrosion or additional undesired erosion during fine-boring at the wall of the bore formed in the workpiece.
Those sections of the tube which are provided with the nonconductive insulating layer may be provided with an electrically conductive metal or graphite layer, to which, as a so-called protective current electrode, an opposite charge to that of the tube made from a metal of substantially amorphous structure may be applied.
According to the present invention, the process for producing an electrode for electrochemical fine-boring includes the steps of providing an electrically conductive metal with a substantially amorphous structure as material for the electrode tube, drawing the electrode tube from a semi-finished tube of larger external diameter to a smaller external diameter by glass drawing, and applying a nonconductive insulating layer at least to sections of its outer surface.